Fig. 2.

(A) Thermal ¹⁵N-¹H imino HMQC correlations acquired for a reference sample containing 350 μM GSR aptamer in 90% H₂O buffer; these data were acquired using four scans per t₁ increment, 128 complex t₁ points, and a recycling delay of 1 s to allow relaxation of imino protons, leading to a 19-min 36-s acquisition. (B) HyperW HMQC spectrum acquired upon sudden injection of hyperpolarized water, using two scans and 37-ms relaxation delay per t₁, yielding a total acquisition time of 43 s for 64 complex t₁ points. The experiment utilized band-selective 90° and 180° ¹H pulses as shown in SI Appendix, Fig. S1B. The final postdissolution RNA concentration was ∼170 μM, and the spectrum was acquired in a ∼2% hyperpolarized H₂O/98% D₂O buffer solution at pH 6.2 and 37 °C. Labeled in red are residues that were undetectable in the thermal experiment—presumably as a result of broadening due to fast exchanges with the solvent.